Did your mods change your gas mileage? I guess, technically, you should be getting better MPG by driving mellow and worse when lead footing, Especially with FI.. throw out some inputs along with your mods, please. I think I've noticed a gain, but not sure. I have:

- popcharger
- plenum spacer

 

I have the mods in my sig (basically all boltons except headers) and my MPG is only 1MPG LOWER on AVG. I used to get 27.5ish on the highway, now I get 26.4ish. Around town I used to get 24ish. Now I get 23ish.

 

my milage has never got above 17 around town and probably never will
but i think i got worse milage after mods just because the noise the car makes is intoxicating

 

This is the theory: holding weight constant, the vehicle with more horsepower will use more fuel.

 

Nismo cat back, Nismo CAI, Mrev and Unichip. I'm pretty sure I lost a couple of mpg. Maybe from 25.5 highway to 23-22.5 with the same kind of driving. Just a guess though. No biggie.

 

It's tough to say. I don't know anyone who has added a mod and then NOT driven the car a bit more aggressive to try to see if they can tell the difference.

The only change I've seen is that on the freeway I get a bit better MPG and the city a bit worse. But freeway driving is constant whereas city is stop and GO-GO-GO!

 

On the highway doing an average speed of 70 I get around 24mpg.
Around the city, stop and go driving and reving higher I only get around 19mpg.